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| Habilitation, Postdoctoral Thesis | PreJuSER-9935 |
2010
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-614-9
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Please use a persistent id in citations: http://hdl.handle.net/2128/3724
Abstract: Since the pioneering papers by Proffitt et al. (1990) and Fahey et al. (1990), tracer-tracer relations have been used in numerous studies to identify physiochemical change in the stratospheric polar vortices. An issue neglected in earlier studies (e.g., M¨uller et al., 1996) is that it is necessary to assess the impact of mixing processes on tracer-tracer relationships in the polar vortex for a reliable quantification of physiochemical change. This neglect has attracted criticism. In particular, the use of ozone-tracer relations was criticised by the argument that mixing processes have the potential to affect ozone tracer relations in a way that leads to an overestimation of chemical ozone loss (Plumb et al., 2000). Specific processes considered were mixing among vortex air masses following differential descent in the vortex, mixing of stratospheric vortex air with a mesospheric intrusion, and mixing of vortex air with out-of-vortex air by mixing across the transport barrier at the vortex edge. Here, it has been shown that differential descent within the vortex and the subsequent mixing among vortex air masses cannot have a significant impact on ozone-tracer relations (Section 3.3). Further, intrusions of mesospheric air into the stratosphere cannot affect ozone loss estimates if they do not reach the altitudes (∼600 K) up to which the ozonetracer relations are usually employed (e.g., M¨uller et al., 1996; Tilmes et al., 2004) or if the intrusions reach the lower stratosphere before the establishment of the early vortex reference relation, i.e., before late November or December in the northern hemisphere. Ozone mixing ratios in mesospheric air are rather low, less than ∼2 ppm, but because of the short chemical lifetime of ozone in the upper stratosphere and above, ozone mixing ratios of mesospheric air increase photochemically during downward transport (Salawitch et al., 2002). Indeed, observed ozone mixing ratios in air masses influenced by mesospheric air in the lower stratosphere in January and March 2003 are greater than those in the surrounding stratospheric air and clearly greater than those found in the ‘early vortex’ reference relation employed to deduce chemical ozone loss (Section 3.4). Thus, if mesospheric air masses were to reach the lower stratosphere and mix strongly enough so that they could no longer be identified, ozone mixing ratios in the lower stratosphere would increase so that the chemical ozone loss signal would be underestimated. Therefore, intrusions of mesospheric air are unlikely to have a significant impact on ozone loss estimates based on the ozone–tracer relation method and, if they were to have an effect, could only lead to an underestimate of chemical ozone loss. Considering mixing between inside and outside vortex air, it is important to note that these two types of air masses are characterised by different ozone-tracer relationships, with the outside vortex relationships showing greater ozone mixing ratios (and a stronger variability) for the same values of the tracer than inside relationships (Sections 3.2 and 3.3, see also [...]
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